The present technology relates to a power supply monitoring circuit, an AC/DC conversion apparatus and a control method of a power supply monitoring circuit and specifically relates to a power supply monitoring circuit, an AC/DC conversion apparatus and a control method of a power supply monitoring circuit detecting supply stop of AC power.
An AC/DC (Alternating Current/Direct Current) converter is generally used for supplying AC power to electronic equipment operating with direct current. The AC/DC converter converts alternating current into direct current using a PFC (Power Factor Control) circuit and the like containing a block capacitor with large capacity. When power supply from the AC power supply is stopped due to blackout or the like, the electronic equipment as the supply destination is supplied with power for a certain period using energy accumulated in the block capacitor and the like. In case where the electronic equipment as the supply destination should perform shutdown processing and the like in its termination of operation, when supply stop of power from the AC power supply is detected, the AC/DC converter outputs the detection signal to the electronic equipment. According to the detection signal, the electronic equipment can perform the shutdown processing until the power supply from the AC/DC converter is completely stopped. The faster the supply stop of the power is detected by the AC/DC converter, the earlier the shutdown processing starts, this enabling to reduce time during which the AC/DC converter should continue the power supply. The shorter the time during which the power supply should be continued is, the smaller the capacity of the block capacitor or the like has to be. Therefore, the supply stop of the AC power is desirable to be detected quickly.
In order to detect supply stop of AC power, for example, a power supply apparatus is proposed which performs full-wave rectification on alternating current to generate a pulsating flow, holds the peak voltage of the pulsating flow in a capacitor and compares voltage of the pulsating flow with a reference voltage as a voltage obtained by voltage-division on the peak voltage (for example, see Japanese Patent Laid-Open No. 2010-261862). The power supply apparatus detects the supply stop of AC power when the state that the voltage of the pulsating flow is lower than the reference voltage continues longer than a predetermined time.
The capacitor, however, continuing to hold the peak voltage still after the supply stop of the power results in the power supply apparatus determining the supply stop of AC power for a long period even when the amplitude of the voltage of the pulsating flow merely declines without stop of the power supply. This is hereinafter referred to as “misdetection”. Therefore, upon the supply stop of AC power, such a power supply apparatus performs forced discharge on the capacitor which holds the peak voltage to shorten a period of the misdetection of supply stop of AC power.